Thank you, Minuteman.
That is indeed the crucial question with regard to most paintings. We have to keep in mind that these were commercial products, executed to please the client. So there's always the danger of something fanciful being added to the painting. That said, they remain a valuable source of information.
As to yellow dragoons: Lesparre were present at Oudenaarde, Listenois at Blenheim and Malplaquet, and Mestre de Camp Général at all four of Marlborough's major battles (if we assume they retained their old uniforms). Some time ago I made a list of all regiments that participated in these battles from the available orders of battle to see which ones I might paint, comes in handy :slightly_smiling_face:.
Letrun's book on the French dragoons (Vol. 1, 1669-1749) is a good source of information and well worth buying.
For anyone interested in something else here's a link to the order of battle of Almanza